Catheter introducers are used commonly to provide percutaneous access to a blood vessel in order to facilitate insertion of catheters into and manipulation within the blood vessel without requiring a separate percutaneous or vessel puncture for each catheter. A typical catheter introducer may be considered as having a relatively short tubular sheath, open at its distal end (the end within the patient), and a housing attached to the proximal end (outside of the patient) of the sheath. The housing typically includes a proximal aperture through which a catheter can be passed as well as a self-sealing valve or gasket to effect a seal to prevent blood from leaking out of the introducer, both when a catheter is passed through the introducer as well as when the catheter has been withdrawn from the introducer. The housing also may include a side port through which blood may be sampled or medication or other physiological liquids may be introduced. Such catheter introducers are in common use in angiography and angioplasty as well as other procedures.
The introducer typically is provided in an assembly with a tubular dilator, on which the introducer is mounted. The dilator is longer than the sheath and housing and passes through the housing so that its distal and proximal ends protrude beyond the distal and proximal ends of the sheath and housing, respectively. The distal protruding end of the dilator is tapered to facilitate advancement through tissue. The proximal end of the dilator typically is provided with a hub that is engageable with the housing. The dilator includes a central lumen that extends fully from its proximal to its distal end and receives a guidewire used in connection with percutaneous placement of the catheter-dilator assembly.
Such dilators typically are placed by the Seldinger technique in which a hollow needle first is advanced through the skin, the subcutaneous tissue and into the blood vessel of interest. A guidewire then is advanced through the hollow needle and into the blood vessel. While maintaining that position of the guidewire, the needle then is withdrawn proximally and is separated from the guidewire. With the sheath mounted on the dilator, the dilator then is threaded onto the proximal end of the guidewire and is advanced along the guidewire toward and into engagement with the puncture site. The distal tapered end of the dilator facilitates insertion of the tip of the dilator into the puncture by progressively dilating the puncture as the dilator is advanced through the tissue. Such progressive dilation of the puncture site is intended to facilitate advancement of the still larger diameter introducer sheath into and through the puncture site so that together they can be advanced along the guidewire into the blood vessel. When the distal portion of the sheath has been advanced into the blood vessel, the dilator and guidewire can be removed, leaving the catheter introducer in place and in readiness to receive and direct other guidewires, catheters or other appropriate instruments into and from the blood vessel.
Among the difficulties commonly encountered in the design and use of catheter introducers is to provide a dilator-sheath combination that can be advanced through tissue with minimal patient discomfort and tissue trauma while also avoiding damage to the introducer. Such difficulties typically occur at the transition region between the guidewire and the dilator tip as well as the transition region between the outer diameter of the dilator and the distal end of the sheath. The dilator-introducer sheath assemblies typically present distally facing shoulders at those transitions. Although the radial extent of the shoulders can be minimized by tapering the distal end of the sheath and the dilator to a thin feathered edge, that presents additional difficulties in that the thinning of the wall of the tube increases substantially the risk that the thin edge will curl back when it engages tissue, resulting in substantially increased resistance to advancement and attendant patient discomfort and tissue trauma.
The prior art has recognized these difficulties and has suggested a number of proposed remedies. Among the proposals has been to configure the distal end of the dilator tip to define a proximally facing shoulder behind which the tip of the dilator sheath can be protected as the assembly is advanced through the tissue. For example, U.S. Pat. No. 5,098,393 (Amplatz) and U.S. Pat. No. 5,499,975 (Cope) disclose such introducer assemblies. In general, the object of such arrowhead-like designs is to improve the transition between the sheath and the dilator and, in some cases, between the dilator and the guidewire. Among the difficulties presented by the arrowhead-type of design is that the smoother the transition between the dilator and sheath, the more difficult it is to withdraw the dilator through the sheath and the greater the risk that such withdrawal may damage the tip of the sheath. A very thin, feathered leading edge for the sheath could develop a small split and could break off into the blood stream. The damaged sheath tip could present sharp edges for corners that could injure the delicate inner lining of the blood vessel. A very thin walled delicate tip for the sheath could become bent inwardly, possibly from withdrawal of the dilator, presenting an inwardly projecting sharp edge that could injure a delicate balloon of a balloon catheter or other catheter component adapted to be inserted through the introducer. It would be desirable to provide a dilator-mounted introducer sheath having an arrowhead design for smooth insertion through the tissue in which the assembly can be advanced percutaneously and smoothly to and through the tissue yet in which the dilator can be removed smoothly and with minimal risk of damage to the tip of the sheath. It is among the objects of the present invention to provide such a sheath-dilator configuration as well as improved techniques for making such devices.
Another aspect of the invention relates to the design and construction of the housing at the proximal end of the introducer sheath and the manner in which the two are joined. Catheter introducer housings are employed in the prior art typically have a body and a proximal end cap that mate to engage and secure the hemostasis gasket within the housing. The body typically is connected to the proximal end of the sheath using one or more techniques including heat, ultrasonic bonding, adhesives, insert molding, among others. Representative of such assemblies are described in U.S. Pat. No. 4,000,739 (Stevens), U.S. Pat. No. 4,424,833 (Spector), U.S. Pat. No. 5,304,156 (Sylvanowicz) and U.S. Pat. No. 5,613,956 (Patterson). In general, such prior techniques require the use of special, expensive equipment, such as ultrasonic welders, and can be somewhat labor intensive. Although the desirability of a snap-on proximal end cap has been incorporated into commercial catheter introducers, the snap-on configuration includes a substantially fully circumferential undercut that may present somewhat of a tendency to separate when the device is in use. It would be desirable to provide an improved, more secure connection between the proximal end cap and the body of the housing. More generally, it would be desirable to provide an improved housing design for a catheter introducer that facilitates more efficient, simplified manufacture and assembly of catheter introducers.